Display screen or a portion thereof with an express chat graphical user interface



The FIGURE is a front view of a display screen or a portion thereof with an express chat graphical user interface.

The peripheral broken line rectangle showing the display screen, or a portion thereof, and all other broken lines showing portions of the express chat graphical user interface are included for the purpose of illustrating portions of the article and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with an express chat graphical user interface, as shown and described. 